Radial nerve anatomy at the level of the humerus.
The lateral intermuscular septum of the arm is formed by a convergence of the deep fascial surrounding the musculature, through which the radial nerve must pass. At the site of perforation, the radial nerve may become entrapped.
The radial nerve takes a spiral course over the mid-humerus, passing from anterior to posterior proximally, wrapping around the medial head of the triceps deep to the lateral head, and then moves anterior again distally as it passes thorough the lateral intermuscular septum. The lateral head is partially transparent to show this course.